Conventionally, various improvements have been made about a scheme for enabling high-speed packet transmission on a downlink from a radio base station to a communication terminal (e.g., HSDPA (High Speed Downlink Packet Access)). This entails an expansion which enables large-volume or low delay data transmission on an uplink channel from the communication terminal to the radio base station, too, and studies on a scheme for realizing high-speed packet communication on an uplink channel (e.g., Enhanced Uplink DCH) are underway.
As with the downlink, studies on the introduction of a scheduling technology for an expansion of such high-speed packet communication to an uplink channel are also underway. The base station carries out scheduling on uplink packets and the base station sends scheduling information created to each communication terminal. Each communication terminal transmits uplink packets to the base station based on the scheduling information received from the base station.
As the scheduling method by the base station, there are proposals on a method called “Base-station Controlled Scheduled Transmission” and a method called “Base-station Controlled Rate Scheduling.”
Of these methods, the method called “Base-station Controlled Scheduled Transmission” is similar to scheduling when high-speed packet transmission is performed on a downlink such as HSDPA. That is, the base station selects several communication terminals for transmitting uplink channel packets and instructs only the selected communication terminals on a (maximum) transmission rate or transmit power margin, etc.
A method of transmitting control information such as scheduling information from the base station to each communication terminal (hereinafter this may be referred to as “downlink control information”) in this case is described in “3GPP, R1-030067, “Reducing control channel overhead for Enhanced Uplink” (hereinafter this will be referred to as “Document 1”). This method is for transmitting downlink control information for each communication terminal selected by scheduling using a downlink channel called “Downlink Scheduling Assignment Control Channel.” That control information consists of transmission timing information, transmit power margin information, identification number for identifying the destination communication terminal (included in a CRC) and a Tail bit for coding.
The method called “Base-station Controlled Rate Scheduling” also causes the base station to assume the responsibility for rate control in uplink channel packet transmission which used to be carried out at a relatively low speed by an RNC (Radio Network Controller) so as to perform rate control at a high speed. This rate control can be realized with additions of a relatively small number of functions for a communication terminal and an improvement of throughput is also expected on the other hand, and therefore this can be considered as an effective method.
This rate control method is explained in “3GPP, R1-03-0129, Two Threshold NodeB Packet Scheduling” (hereinafter referred to as “Document 2”). More specifically, by sending control information instructing an increase/decrease of a transmission rate made up of Up/Down/Keep called “RG (Rate Grant) information” to all communication terminals carrying out uplink packet transmission, the base station controls a maximum transmission rate of each communication terminal individually. Since a Keep command can be expressed by “not transmitting RG information (no transmission)”, it is possible to actually send Up/Down. The communication terminal transmits uplink packets at a maximum transmission rate or below in consideration of a transmit power margin and amount of data. However, transmitting these two values of Up/Down is only an example and it is also possible to instruct an increase/decrease of the transmission rate in further detail if downlink control information can transmit a plurality of bits.
The aforementioned Document 2 describes that it is also possible to apply a technology of hybrid ARQ, etc., at the same time. That is, downlink control information to be transmitted from a base station to a communication terminal can be ACK/NACK of hybrid ARQ, etc., in addition to RG information.
In uplink packet transmission using “Base-station Controlled Rate Scheduling”, improvements in actually transmitting downlink control information are described in the “3GPP, R1-030177, Downlink physical channel structure” (hereinafter referred to as “Document 3”). This Document 3 describes a method of transmitting downlink control information embedded in a dedicated channel for each communication terminal such as DPDCH (Dedicated Physical Data channel) or DPCCH (Dedicated Physical Control Channel).
FIG. 1 shows a configuration example of a radio base station apparatus for realizing this method. First, the transmission system of a radio base station apparatus 10 will be explained. The radio base station apparatus 10 is provided with a plurality of dedicated channel signal formation units 11-1 to 11-N that form transmission signals directed to their respective communication terminal apparatuses. That is, there are N dedicated channel signal formation units 11-1 to 11-N corresponding to N communication terminals with which they communicate. Since processes of the respective dedicated channel signal formation units 11-1 to 11-N are the same, the configuration of only one dedicated channel signal formation unit 11-1 will be explained here.
The dedicated channel signal formation unit 11-1 multiplexes a pilot signal (PILOT), transmission data, uplink channel transmit power control command (UL-TPC), ACK/NACK and RG information through a channel encoding section 12. Before being multiplexed, the transmission data is subjected to error correcting coding. The multiplexed signal is modulated by a modulation section 13 and sent to a spreading section 14.
The spreading section 14 carries out spreading processing on the modulated signal using a spreading code specific to the communication terminal. That is, the dedicated channel signal formation units 11-1 to 11-N carry out spreading processing using different spreading codes. The spread signal is sent to an amplification section 15. The amplification section 15 increases/decreases power of the spread signal according to a transmit power control signal from a transmit power control section 16 and sends the amplified signal to a transmission radio section 17.
In this way, the dedicated channel signals specific to the respective communication terminals obtained from the dedicated channel signal formation units 11-1 to 11-N using different spreading codes are output. The dedicated channel signals are subjected to predetermined radio processing such as analog/digital conversion and up-conversion, etc., by the transmission radio section 17 and transmitted through an antenna 18.
Next, the reception system of the radio base station apparatus 10 will be explained. The radio base station apparatus 10 inputs a signal received from the antenna 18 to a reception radio section 20. The reception radio section 20 carries out predetermined radio processing such as down-conversion and analog/digital conversion on the received signal to obtain a received baseband signal and sends this baseband signal to reception processing units 21-1 to 21-N provided for the N communication terminals. Since processes of the dedicated channel signal formation units 21-1 to 21-N are the same, only the configuration of the dedicated channel signal formation unit 21-1 will be explained here.
A despreading section 22 carries out despreading processing on the received baseband signal using a spreading code corresponding to the communication terminal, extracts a dedicated channel signal sent from the communication terminal apparatus and outputs the dedicated channel signal to a demodulation section 23. Furthermore, the despreading section 22 sends information indicating desired signal power obtained from a delay profile to be created during dispreading to an SIR measuring section 29.
The demodulation section 23 carries out demodulation processing on the output signal of the despreading section 22 and sends the demodulated signal to a channel decoding section 24. The channel decoding section 24 carries out decoding processing such as error correcting decoding on the output signal of the demodulation section 23 and extracts received data, downlink transmit power control command (DL-TPC), etc. The received data is sent to a higher level control station and the DL-TPC is sent to the transmit power control section 16.
The SIR measuring section 29 calculates interference signal power from a variance of the desired signal power, calculates a ratio (SIR) of the desired signal power to the interference signal power and sends information indicating the SIR to the TPC generation section 30 and scheduling section 32. The TPC generation section 30 generates an uplink channel transmit power control command (UL-TPC) for instructing an increase/decrease of transmit power of the uplink channel based on a magnitude relationship between a reception SIR and target SIR of the uplink channel and sends this UL-TPC to the channel encoding section 12.
The scheduling section 32 decides a communication terminal apparatus for which transmission of packet data is allowed based on rate request information (RR information) from each communication terminal apparatus, the SIR and a reception power margin from the reception power measuring section 31 and decides parameters (coding rate of error correcting coding, modulation multi-value number, spreading factor, transmit power, etc.) during the packet data transmission as RG information (scheduling). Then, the scheduling section 32 sends this RG information to the channel encoding section.
The reception power measuring section 31 calculates a reception power margin based on reception power from the reception radio section 20 and maximum reception power and sends the reception power margin to the scheduling section 32.
A despreading section 25 carries out despreading processing on the received baseband signal using the same spreading factor as that used for spreading the uplink packet data by the communication terminal. Information such as the spreading factor of this uplink packet data, modulation multi-value number, coding rate, etc., is embedded in the signal by the communication terminal and transmitted, and the radio base station apparatus 10 extracts the information embedded in the received data and notifies the despreading section 25, demodulation section 26 and channel decoding section 27 of the information. That is, the despreading section 25, demodulation section 26 and channel decoding section 27 are constructed so as to be able to change the spreading factor, modulation multi-value number and coding rate according to the transmission parameter information from the communication terminal.
The demodulation section 26 carries out demodulation processing on the packet signal output from the despreading section 25 and sends the demodulated signal to the channel decoding section 27. The channel decoding section 27 carries out decoding processing such as error correcting decoding on the demodulated signal, extracts received packet data and outputs the packet data to an error detection section 28. Furthermore, the channel decoding section 27 extracts rate request information (RR information) and sends the rate request information to the scheduling section 32.
The error detection section 28 carries out error detection on the received packet data. When no error is detected, the error detection section 28 outputs the received packet data to a higher level station and sends an ACK signal indicating that the data has been demodulated correctly to the channel encoding section 12. On the other hand, when an error is detected, the error detection section 28 sends a NACK signal indicating that the data has not been demodulated correctly to the channel encoding section 12.
FIG. 2 shows the configuration of a communication terminal apparatus which communicates with the radio base station apparatus 10. The communication terminal apparatus 40 inputs a signal received through an antenna 41 to a reception radio section 42. The reception radio section 42 applies down-conversion and analog/digital conversion processing on the received signal to obtain a received baseband signal and sends this baseband signal to a despreading section 43.
The despreading section 43 carries out despreading processing using a spreading code specific to this communication terminal to obtain a signal directed to the own station. The despread signal is subjected to demodulation processing and decoding processing sequentially by a demodulation section 44 and a channel decoding section 45, and received data, uplink channel transmit power control command (UL-TPC), transmission rate information (RG information) and ACK/NACK are thereby obtained. Furthermore, the despread signal is input to an SIR measuring section 46 and a TPC generation section 47 sequentially and a downlink transmit power control command (DL-TPC) is thereby obtained from the TPC generation section 47.
Next, the transmission system of the communication terminal apparatus 40 will be explained. While the communication terminal apparatus 40 changes a coding rate, modulation multi-value number or spreading factor for transmission packet data, the communication terminal apparatus 40 does not change these parameters for other data. More specifically, a pilot signal (PILOT), downlink signal transmit power control command (DL-TPC) or transmission data is processed by a channel encoding section 50, a modulation section 51 and a spreading section 52 whose coding rate, modulation multi-value number and spreading factor are fixed respectively and then the spread signal is sent to an amplification section 53.
On the other hand, the transmission packet data is stored in a buffer 54 first. Based on the ACK/NACK, the buffer 54 erases the transmission packet data transmitted last time and outputs the initial transmission packet data to a channel encoding section 59 in the case of ACK, whereas the buffer 54 outputs the transmission packet data sent last time to the channel encoding section 59 again in the case of NACK.
Furthermore, an amount of transmission packet data stored in the buffer 54 is measured by a data amount measuring section 55 and the data amount measuring section 55 sends the measurement result to a transmission rate selection section 57 and a rate request selection section 56.
The transmission rate selection section 56 selects a transmission rate at which data is actually transmitted based on the RG information sent from the radio base station apparatus 10 and extracted from the channel decoding section 45, that is, transmission rate information, amount of data stored in the buffer 54 and transmit power margin and notifies the rate request selection section 56 of the selected transmission rate and also notifies a transmission parameter setting section 58 of the same.
The rate request selection section 56 generates rate request information (RR information) based on the transmission rate notified from the transmission rate selection section 57, amount of data stored in the buffer 54 and transmit power margin and sends the rate request information to the channel encoding section 59. This RR information is information indicating a transmission rate of transmission packet data desired by the communication terminal apparatus and is expressed by, for example, 1 to n (n is a natural number of 2 or above).
Based on the transmission rate notified from the transmission rate selection section 57, the transmission parameter setting section 58 controls the reading rate of the transmission packet data stored in the buffer 54, sets the coding rate at the channel encoding section 59, modulation multi-value number at a modulation section 60 and the spreading factor at a spreading section 61 and sends these transmission parameters to the channel encoding section 59, modulation section 60 and spreading section 61. Furthermore, based on the transmission rate, the transmission parameter setting section 58 sets an amount of offset of transmit power when packet data is transmitted and sends this amount to a transmit power control section 63.
The transmit power margin input to the transmission rate selection section 57 and rate request selection section 56 is set by a transmit power measuring section 65. More specifically, the transmit power measuring section 65 sets the transmit power margin based on transmit power controlled by a transmit power control section 64 according to an uplink channel transmit power control command (UL-TPC) and maximum transmit power that can be transmitted by the own apparatus. The transmit power control section 63 that generates a transmit power control signal of packet data generates a transmit power control signal which is obtaining by giving an offset set by the transmission parameter setting section 58 to the control signals from the transmit power control section 64 such as other pilot signal, downlink transmit power control command (DL-TPC) and transmit power control signal of transmission data.
The spread signals output from the spreading section 52 and spreading section 61 are amplified independently by corresponding amplification sections 53, 62, subjected to predetermined radio processing such as digital/analog conversion and up-conversion by a transmission radio section 66 and transmitted through the antenna 41.
In the conventional radio base station apparatus 10 and communication terminal apparatus 40 having the structures shown in FIG. 1 and FIG. 2, the radio base station apparatus 10 transmits control information for uplink packet transmission such as RG information and ACK/NACK embedded in a dedicated channel. The communication terminal apparatus 40 extracts a control signal directed to the own station from the received signal by despreading the received signal using a dedicated spreading code. Then, the communication terminal apparatus 40 decides the transmission rate of transmission packet data or whether retransmission is necessary or not based on this control signal and forms an uplink packet signal.
FIG. 3 shows the states of the respective dedicated channels transmitted from the radio base station apparatus 10. Dedicated channel signals (communication terminal 1 dedicated ch to communication terminal N dedicated ch) directed to the communication terminals 1 to N are formed by the aforementioned dedicated channel signal formation units 11-1 to 11-N. In each dedicated channel, control information for forming uplink packet signals such as RG information and ACK/NACK expressed by shaded areas in the figure is embedded between transmission data. Here, each dedicated channel is spread using a spreading code specific to each communication terminal, and therefore even if a plurality of dedicated channel signals is received at the same time, each communication terminal can extract only the transmission data and control information directed to the own station and can form an uplink packet signal adequately based on the extracted control information.
When control information (downlink control information) for forming an uplink packet signal is transmitted using a method shown in “3GPP, R1-030067, “Reducing control channel overhead for Enhanced Uplink” if information is transmitted only to a selected communication terminal through scheduling as a method called “Base-station Controlled Scheduled Transmission”, there should be only the same number of downlink channels for transmitting control information as the selected communication terminals.
However, when downlink control information is transmitted to all communication terminals simultaneously as in the case of a method called “Base-station Controlled Rate Scheduling”, downlink control information channels corresponding in number to all the communication terminals are required. As a result, there is a problem that resources of downlink spreading codes are overconsumed.
Furthermore, in the method called “Base-station Controlled Rate Scheduling”, even if only control information indicating an increase/decrease of a transmission rate is sent, it is necessary to add numbers for identifying to which communication terminal the control information is directed to the control information. This causes a problem that overhead increases and transmit power resources on a downlink are overconsumed. Furthermore, when downlink transmit power resources are overconsumed, interference with other cells increases, leading to a reduction of a system capacity.
On the other hand, as indicated in “3GPP, R1-030177, Downlink physical channel structure”, that is, as is implemented with the configurations shown in FIG. 1 and FIG. 2, when the downlink control information for forming an uplink packet signal is embedded in a dedicated channel of each communication terminal which is carrying out uplink packet transmission, it is possible to transmit control information to all communication terminals, but there is also a problem of producing adverse effects on existing dedicated channels. Moreover, transmitting downlink control information embedded in the existing dedicated channels without errors needs to increase transmit power of the downlink control information, which results in a problem that the downlink transmit power resources are overconsumed.
For example, when control information is embedded in a data channel called “DPDCH” (channel to mainly transmit speech data and signaling, etc., from a higher level apparatus), the number of bits on a physical channel available for dedicated channel data is decreased, which leads to a problem that the quality of transmission data deteriorates. Compensating for this quality deterioration requires transmit power of a dedicated channel to be increased.
Furthermore, when control information is embedded in a control channel called “DPCCH”, there is a proposal on assignment of the bit of TFCI (used to notify the receiving side of the data size of a plurality of channels multiplexed in the DPDCH” to this control information. But this also deteriorates the reception performance of TFCI, increasing the probability that reception processing of dedicated channels will not be performed correctly.
Furthermore, when a standardization specification using dedicated channels is already determined, changing the standardization specification of a downlink dedicated channel produces another problem that not only a test on uplink channel packet transmission but also a test on dedicated channels needs to be done again.